Attempts will be made to evaluate the physiological and quantitative significance of mitochondria to the intracellular synthesis of fatty acids and glycerolipids. Studies on the mechanism of action and control of the enzymes involved in the substrate and positionally specific synthesis of phosphatidic acid will be continued. Promising leads on the mechanism and control of fatty acid elongation in mitochondria will be pursued in an attempt to develop them into facts. These studies will include experiments designed to demonstrate that the fatty acid elongation system is different from the beta-oxidation enzymes and to confirm evidence on hand that suggests on the one hand that this enzyme system exists in the mitochondrial membrane as a multienzyme complex and on the other, that the increased efficiency offered by this structural assemblage is essential to the mechanism of the thermodynamically unfavorable initial condensation step.